Load cell mounting apparatus and method

ABSTRACT

A load cell alignment apparatus for aligning a load cell during an axial tension test of a brake cable. The apparatus includes a mounting structure, an alignment structure, a biasing device, and the load cell. The alignment structure is connected between the mounting structure and the biasing device. The biasing device is connected to the load cell and applies a tension preload to the load cell, and the alignment structure, in response to the tension preload, properly aligns the load cell with an axis for subsequent measurement of applied tension on the brake cable. The alignment structure permits only linear axial tension to be applied to the load cell in response to application of a further tension load on the load cell.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a mounting for a loadcell and, more specifically, to a load cell mounting method andapparatus to facilitate accurate measurement of an automotive brakecable tension.

[0003] 2. Description of Related Art

[0004] In automobile manufacture, automotive parts are routinely tested.The parts are tested during the research and development stage ofautomotive design, and the parts are tested later for quality assurancepurposes.

[0005] In a test of an automotive brake system, a brake cable in a brakeassembly is tension loaded. The tension load on the brake cable ismeasured to determine the tension load applied to the brake cable at thebrake handle and the tension force delivered to the brake assembly.These two tension measurements are used to determine the efficiency ofthe brake cable assembly and to determine whether sufficient brakingforce is delivered to the brake assembly by the brake cable.

[0006] It is desirable to produce an accurate proportional relationshipbetween the strain on the brake assembly and the applied load, andthereby to measure the absolute tension transferred by the brake cableto the brake assembly. However, factors such as non-linearity,hysteresis and temperature effects on a load cell can create errors anddecrease the accuracy of the measurement.

[0007] Non-linearity errors are the result of the brake cable beingmisaligned with the device that is provided to measure the tension onthe cable. Such non-alignment creates side tension loads that are atangles to the axis of the cable. These side loads have several vectorcomponents. A first vector component is parallel to the axis andcontributes to the axial tension load. However, other vector componentsare skewed from the axis and do not add to the axial tension load.Introduction of such side loads will result in incorrect measurements ofthe forces applied to the brake assembly. As such, during testing ofbrake cable assemblies, misalignment of testing components is a commonsource of measurement error.

[0008] Therefore, there exists a need in the art for a method andassembly to accurately align the brake components and, morespecifically, the testing components, so as to eliminate the effects ofside loading and thereby obtain more accurate measurement of tensionforces on the brake cable at the brake assemblies.

SUMMARY OF THE INVENTION

[0009] The present invention is directed toward a method and assembly toaccurately align the testing components with an axis of a brake cable.The present invention is further directed toward a method and assemblyto eliminate the effects of side loading on a brake cable so as toaccurately measure the tension force applied by the brake cable.

[0010] The present invention provides a load cell alignment apparatusfor aligning a load cell during testing of a brake cable assembly. Theapparatus includes a mounting structure, and an alignment structuresecured between the mounting structure and the load cell. The alignmentstructure ensures that only axial tension is applied to the load cellduring a testing procedure.

[0011] The present invention also provides a method of automaticallyaligning a load cell on a load cell axis during a tension test of acable. The method includes providing an alignment structure thatautomatically aligns the load cell on the load cell axis duringapplication of a tension load. The method also includes applying atension load to the load cell and using the applied tension toautomatically align the load cell and cable on the load cell axis.

[0012] The present invention further provides a method for measuring abrake cable efficiency. The method includes applying a first force to abrake handle so as to create a second, subsequent force at a brake hub.The first force and the second force are measured. The first and secondforce measurements are compared to determine the brake cable efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] These and further features of the invention will be apparent withreference to the following description and drawings, wherein:

[0014]FIG. 1 is a schematic view of a system comprising a firstembodiment of the invention;

[0015]FIG. 2 is an enlarged schematic view of an apparatus comprising aportion of the system shown in FIG. 1;

[0016]FIG. 3 is a schematic cross-sectional view of a portion of theapparatus shown in FIG. 2; and

[0017]FIG. 4 is a schematic view of an apparatus comprising a secondembodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0018] A load cell mounting system 100 comprising a first embodiment ofthe invention is shown in FIG. 1. The system 100 properly aligns a loadcell with a cable during tension load testing of the cable, and therebyto eliminate or minimize side loading of the cable that could interferewith the accuracy of the test results. Specifically, the illustratedsystem 100 is used to apply a tension load on an automotive brake cableand to measure the amount of braking force (cable tension) delivered tothe brakes.

[0019] The system 100 includes a parking brake handle 102 and a handleload cell 104. The handle load cell 104 measures a force exerted on theparking brake handle 102. The measurement information is forwarded to acomputer or display device (not shown). Movement of the parking brakehandle 102 is communicated to a force equalizer 106, which in turnapplies a tension load to two brake cables 108.

[0020] One end of each cable 108 connects to the equalizer 106, whilethe opposite end of each cable 108 connects to a respective cableadaptor 120. The cable adaptor 120 represents the point where the cable108 would attach to a brake assembly in an automobile. Thus, a force ortension load applied to the cable adaptor 120 is equivalent to a forceor tension load applied to an automobile brake assembly.

[0021] The cable 108 is preferably a non-elastic cable with a metalstrand core. The cable 108 has both a low level of stretch and of torquein response to the application of a tension load.

[0022] A load cell 122 communicates with the cable adaptor 120 through acable 124. The cable 124 and the load cell 122 are linearly aligned witheach other and centered on an axis 125. The load cell 122 alsocommunicates with a biasing apparatus 126 through a threaded rod 128,which is likewise linearly aligned with and centered on the axis 125.

[0023] In this embodiment, the load cell 122, also called a forcetransducer, operates on the principle that the resistance of apiezoresistor will increase when the piezoresistor flexes under anapplied force. The load cell 122 concentrates an applied force, througha plunger, directly to a silicon-based sensing element. The amount ofresistance changes in proportion to the amount of force applied. Thischange in the resistance results in a corresponding change in thevoltage (V) output level. Suitable load cells are commercially availablefrom, for example, Honeywell Sensing and Control, Inc. (Freeport, Ill.).

[0024] A strain amplifier 130 communicates with the load cell 122through a wire 132. The strain amplifier 130 includes an LCD digitaldisplay and further communicates with a computer (not shown). The strainamplifier 130 sends an excitation voltage to the load cell 122 andconditions the return signal.

[0025] An alignment structure 136 communicates with both the biasingapparatus 126 and a mounting structure 140. The mounting structure 140mounts on a surface 142. The biasing apparatus 126, the alignmentstructure 136 and the mounting structure 140 together form a mountingassembly 146.

[0026] With reference to FIG. 2, the mounting assembly 146 includes thebiasing apparatus 126 that communicates with the load cell 122 throughthe rod 128, as described above. The rod 128 is a stud that extends intoa first end cap 160 of the biasing apparatus 126 and has a nut assembly152 threaded thereto at a first threaded portion 154. The rod 128 isthreaded into the load cell 122 at a second threaded portion 156,opposite the first threaded portion 154 (FIG. 1). Accordingly, both thenut assembly 152 and the load cell 122 define threaded apertures thatreceive the rod 128.

[0027] The alignment structure 136 fastens to a second endcap 164, whichis connected to an end of the biasing apparatus 126. The second endcap164 and a jam nut 165 each define an aperture. The alignment structure136 includes a rod 166 threaded at a first end that extends through theapertures defined by the jam nut 165 and the second endcap 164 and intothe biasing apparatus 126. A non-threaded second end of the rod 166connects with a ball joint assembly 168.

[0028] The ball joint assembly 168 includes a threaded portion 170 and aball joint 174. The threaded portion 170 threads into a threadedaperture 172 in the mounting block 140. The ball joint 174 is acommercially available, steel ball-and-socket type ball joint. The balljoint 174 preferably has a low-friction polymeric inner sleeve, as knownto one skilled in the art.

[0029] The mounting structure 140 has a plurality of boltholes 176 thatalign with boltholes (not shown) in the mounting surface 142. Bolts (notshown) extend through the boltholes 176 and further through the mountingsurface 142 to secure the mounting structure 140 to the mounting surface142.

[0030] With reference to FIG. 3, the biasing apparatus 126 includes acylindrical main body 180 that is threaded at first and second ends. Thefirst endcap 160 threadedly secures to the first threaded end, and thesecond endcap 164 threadedly secures to the second threaded end,opposite the first threaded end. The nut assembly 152 includes a pair ofnuts and a washer adjacent the first endcap 160 on the biasing apparatus126. The rod 128 extends through the nut assembly 152, and through anaperture in the first endcap 160, into the main body 180. Accordingly,the nut assembly 152 threadedly secures the rod 152 to the first endcap160.

[0031] The rod 166 extends into the cylindrical main body 180, asdescribed above. A nut 185 threadedly secures a washer 186 to an end therod 166.

[0032] The main body 180 houses a spring 188. The spring 188 wrapsaround the rod 166 and is disposed between the second endcap 164 and thewasher 186. The jam nut 165 is wider than the aperture in the secondendcap 164. Accordingly, the second endcap 164 and the washer 186 retainthe spring 188 in a compressed condition. Further, the rod 166 can movelongitudinally while influenced by the bias of the spring 188.

[0033] During operation, the jam nut 165 is rotated, if desired, to movethe rod 166 relative to the second endcap 164 and adjust the compressionof the spring 188. The second endcap 164 and the washer 186 compress thespring 188, and with the jam nut 165, maintain the desired springcompression. The spring compression establishes a preload or biasingtension on the load cell 122. In response to the preload tension, thejoint 168 swivels, rotates to align the load cell 122 with the axis 125and thereby minimizes or eliminates tension side loading on the loadcell 122.

[0034] When the tension testing begins, a force is applied to the handle102 and is measured by the load cell 104. Information about the force iscommunicated to the computer. The force on the handle 102 is distributedby the equalizer 106 equally to each cable 108, thus the equalizer 106applies a tension load to each cable 108.

[0035] The cable 108 communicates the tension load to the cable adaptor120. In response, the cable adaptor 120 communicates the tension load tothe load cell 122 through the rod 124. The joint 168 swivels, rotatesand otherwise adjusts to align the load cell 122 with the axis 125,minimizing or eliminating tension side loading on the load cell 122.Accordingly, the applied tension load on the load cell 122 is an axialtension load only and the load cell 122 can thus selectively measure theaxial tension load.

[0036] The load cell 122 generates a signal in response to the tensionload. The wire 132 communicates the signal to the strain amplifier 130to indicate the tension load placed on the load cell 122. The strainamplifier 130 displays information about the tension load in response tothe signal. Further, the computer can also compare the force measurementinformation of the load cell 104 with the tension load measurementinformation of the load cell 122. The computer can determine thedifference between the measurements and calculate both an absolutetension load on the load cell 122 and a differential tension load withrespect to the applied force on the handle 102 and the resultant tensionload on the load cell 122. Such information will be used to determinethe efficiency of force transfer from the brake handle to the brake hub.A predetermined range of acceptable brake efficiency values are comparedwith the measured brake efficiency value to determine whether sufficientforce is being applied to the brakes to engage the brake pads with thebrake drum.

[0037]FIG. 4 shows an apparatus 300 according to a second embodiment ofthe invention. The apparatus 300 includes many parts that aresubstantially the same as corresponding parts of the mounting apparatus146; this is indicated by the use of the same reference numerals inFIGS. 1 and 4. The apparatus 300 differs in that it includes a universaljoint 302 rather than the ball joint 168. The universal joint 302connects the biasing apparatus 126 to the mounting block 140.

[0038] During operation, the universal joint 302 swivels, rotates andotherwise adjusts to reduce or eliminate tension side loading on theload cell 122. Accordingly, the only tension load on the load cell 122is an axial tension load.

[0039] The load cell 122 generates a signal in response to the axialtension load. The wire 132 communicates the signal to the strainamplifier 130. A sensor (not shown) measures variables, such as thetemperature, and communicates with the strain amplifier 130. The strainamplifier 130 displays information about the tension load in response tothe signal and the other measured variables.

[0040] The embodiments described herein are examples of structures,systems and methods having elements corresponding to the elements of theinvention recited in the claims. This written description may enablethose skilled in the art to make and use embodiments having alternativeelements that likewise correspond to the elements of the inventionrecited in the claims. The intended scope of the invention thus includesother structures, systems and methods that do not differ from theliteral language of the claims, and further includes other structures,systems and methods with insubstantial differences from the literallanguage of the claims.

What is claimed is:
 1. A load cell alignment apparatus for aligning aload cell during a tension test of a brake system, comprising: amounting structure operable to mount to a surface; and an alignmentstructure connected between the mounting structure and the load cell,the alignment structure being configured to permit only linear axialtension to be applied to the load cell in response to a tension loadapplied to the brake system, whereby the load cell measures the linearaxial tension load applied to the load cell.
 2. The apparatus as definedin claim 1, wherein the alignment structure includes a biasingapparatus, the biasing apparatus being operable to apply a preloadtension to the load cell and to maintain the preload tension on the loadcell during the tension test of the brake system.
 3. The apparatus asdefined in claim 2, wherein the biasing apparatus comprises a mainhousing having first and second ends, the biasing apparatus furthercomprising a first cap on the first end, and a second cap on the secondend, the first cap defining an aperture; a spring inside the housingbeing disposed between the first and second caps; a stud having athreaded portion, an extended portion and a washer, the threaded portionthreadedly connecting the stud to the load cell, the extended portionextending through the aperture and further through the spring, and thewasher being disposed in the housing between the spring and the secondcap; and a jam nut on the threaded portion outside of the can body,whereby the jam nut and the washer cooperate with each other to maintainthe spring in a compressed state.
 4. The apparatus as defined in claim1, wherein the alignment structure is a ball joint.
 5. The apparatus asdefined in claim 1, wherein the alignment structure is a universaljoint.
 6. The apparatus as defined in claim 1, further comprising ahandle, and a second load cell communicating with the handle and beingoperable to measure a force applied to the handle and to signal thehandle force measurement.
 7. The apparatus as defined in claim 6,further comprising a device that is operable to receive the linear axialtension load measurement and the handle force measurement, and isfurther operable to compare the linear axial tension load measurementand the handle force measurement.
 8. A method of automatically linearlyaligning a load cell with an axis during a tension test of a brakesystem, comprising the steps of: providing an alignment structureoperatively connected to the load cell, the alignment structure beingoperable to automatically linearly align the load cell with the axis inresponse to a tension load; and applying a first tension load on theload cell and the alignment structure, and thereby automaticallylinearly aligning the load cell with the axis.
 9. The method as definedin claim 8, further comprising the step of generating a signal inresponse to the first tension load, the signal having a signal strengthproportional to the first tension load.
 10. The method as defined inclaim 9, further comprising the step of measuring the signal strength todetermine a first tension load measurement, and displaying the firsttension load measurement.
 11. The method as defined in claim 8, furthercomprising the step of applying a second tension load to the brakesystem, and thereby to apply the second tension load on the load celland the alignment structure, and generating a second signal in responseto the second tension load, the second signal having a second signalstrength proportional to the second tension load, and measuring thesecond signal strength to determine a second tension load measurement.12. An apparatus for automatically linearly aligning a load cell with anaxis during a tension test of a brake system, comprising: means foraligning the load cell with an axis in response to application of atension load on said load cell; and means for applying a first tensionload on the load cell and the alignment structure, and thereby toautomatically linearly align the load cell on the axis.
 13. A system fortesting a tension loading on a cable in an automotive brake system,comprising: a mounting base operable to mount to a surface; and analignment structure connecting the mounting base to the cable; a biasingdevice disposed between the alignment structure and a load cell operableto apply a preload tension to the cable, said biasing device beingoperable to maintain a predetermined preload tension on the cable beforeand during tension testing of the cable; and a load cell disposedbetween the biasing device and the cable and operatively connected tothe cable, said load cell being operable to measure an applied tensionload on the cable during tension testing of the cable, whereby thebiasing device allows longitudinal motion of the cable and the alignmentstructure maintains a linear condition of the cable in response to theapplied tension load on the cable, the linear condition preventing aside tension loading of the cable.
 14. The system as defined in claim13, further comprising a parking brake handle for receiving a force andresponding by applying the applied tension load to the cable, a secondload cell operable to measure the applied tension load, and a computercommunicating with the first and second load cells that is operable tocompare the force with the applied tension load.
 15. A method formeasuring a brake cable efficiency, comprising the steps of: applying afirst force to a brake handle so as to create a second, subsequent forceat a brake hub; measuring the first force; measuring the second force;and comparing the first and second forces to determine the brake cableefficiency.
 16. The method as defined in claim 15, further comprisingthe step of minimizing side loadings on the cable.
 17. The method asdefined in claim 15, further comprising the step of aligning the cable.18. The method as defined in claim 15, further comprising the step ofcomparing the determined brake cable efficiency to a predetermined rangeof acceptable brake cable efficiency values.